1. Field of the Invention
The invention in general relate to the field of medical or therapeutic lavage, and more particularly to a mechanized lavage system in which the rate of fluid flow and the average fluid pressure are variable.
2. Description of the Prior Art
Lavage, or the washing of tissue, is perhaps as old as medicine itself. In the early years it consisted of the application of fluid, generally a liquid such as water, to tissue to wash away dirt or debris. In more modern times it has become more important, and more thorough, due to an awareness of bacteria and other organisms that may cause infection. In the last several decades, mechanized lavage systems have become common, however many surgeons and other physicians have preferred to use syringes or other hand-operated means for lavage because prior art mechanized systems have not been suitable for delicate and critical cleansing tasks.
Before proceeding to the discussion of prior art mechanized devices it will be useful to clarify terminology. The word "lavage" is used ambiguously in the literature, sometimes referring to a pulsating stream type washing or therapy, sometimes referring to a stream type of washing, and sometimes also including an aspiration function. In this document, unless the context clearly indicates otherwise, "irrigation" shall mean the stream type of washing, "pulsatile lavage" shall mean the pulsating type of washing or therapy, and the word "lavage" shall mean the broadest sense of the term, referring to any one of, or combinations of irrigation, pulsatile lavage, and aspiration. Further, in this document the term "operating condition" condition refers to a thermodynamic variable of the system or a portion of the system, such as pressure, volume, temperature, and pulsation frequency, and any variable directly dependent on these, such as the rate of fluid flow (which depends directly on pressure and volume), or the internal resistance of electric driving motor coils (which depends directly on temperature).
Typical prior art lavage systems are described in U.S. Pat. Nos. 3,912,168 issued to Keith M. Mullins, et al. and 3,993.054 issued to Gordon Arthur Newman. In these systems the frequency of pulsation is generally not variable and the pressure and rate of flow of fluid through the system is controllable only through crude throttle type controls. Such controls are difficult to operate and are prone to producing a sudden unwanted burst of pulsatile flow and/or suction when it was not desired. This needs to happen only once during a critical surgical or other medical operation and the surgeons will return to their more familiar hand operated systems.
U S. Pat. No. 4,299,221 discusses the control problems with the prior art, and attempts to overcome them by using a mechanized valve in the lavage head which is powered by air pressure. In doing so, the device lost to a significant degree the desirable features of simplicity and inexpensive construction which permitted the prior devices to be disposable, which is preferable in devices whose puspose is cleansing open wounds, and also greatly increased the problems of resterilization, which is absolutely necessary in such devices if they are not disposable.
The prior art systems tend toward nonreproducibility of results. That is, different pulsation frequencies and different maximum pressures and rates of flow would be produced by the system depending upon whether it had just been turned on, whether it had been operating for some time, and whether the throttle controls had been closed down and the instrument laid aside while the physician attended to another procedure. For example, a physician might be accustomed to one flow from the system, then turn it off for a moment and find that when he picked it back up again the system provided a somewhat different flow. Similiarily, the flow might change during the course of use, even though the physician did not vary his use of the hand controls.